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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MBONED Working Group H. Asaeda 3 Internet-Draft NICT 4 Intended status: Standards Track K. Meyer 5 Expires: May 4, 2017 Cisco 6 W. Lee, Ed. 7 October 31, 2016 9 Mtrace Version 2: Traceroute Facility for IP Multicast 10 draft-ietf-mboned-mtrace-v2-16 12 Abstract 14 This document describes the IP multicast traceroute facility, named 15 Mtrace version 2 (Mtrace2). Unlike unicast traceroute, Mtrace2 16 requires special implementations on the part of routers. This 17 specification describes the required functionality in multicast 18 routers, as well as how an Mtrace2 client invokes a query and 19 receives a reply. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on May 4, 2017. 38 Copyright Notice 40 Copyright (c) 2016 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 57 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6 58 3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 7 59 3.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . 7 60 3.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . 8 61 3.2.1. Mtrace2 Query . . . . . . . . . . . . . . . . . . . . 8 62 3.2.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . 10 63 3.2.3. Mtrace2 Reply . . . . . . . . . . . . . . . . . . . . 10 64 3.2.4. IPv4 Mtrace2 Standard Response Block . . . . . . . . 11 65 3.2.5. IPv6 Mtrace2 Standard Response Block . . . . . . . . 14 66 3.2.6. Mtrace2 Augmented Response Block . . . . . . . . . . 17 67 3.2.7. Mtrace2 Extended Query Block . . . . . . . . . . . . 18 68 4. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 19 69 4.1. Receiving Mtrace2 Query . . . . . . . . . . . . . . . . . 19 70 4.1.1. Query Packet Verification . . . . . . . . . . . . . . 19 71 4.1.2. Query Normal Processing . . . . . . . . . . . . . . . 20 72 4.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 20 73 4.2.1. Request Packet Verification . . . . . . . . . . . . . 20 74 4.2.2. Request Normal Processing . . . . . . . . . . . . . . 21 75 4.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . 22 76 4.3.1. Destination Address . . . . . . . . . . . . . . . . . 23 77 4.3.2. Source Address . . . . . . . . . . . . . . . . . . . 23 78 4.3.3. Appending Standard Response Block . . . . . . . . . . 23 79 4.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 24 80 4.4.1. Destination Address . . . . . . . . . . . . . . . . . 24 81 4.4.2. Source Address . . . . . . . . . . . . . . . . . . . 24 82 4.4.3. Appending Standard Response Block . . . . . . . . . . 24 83 4.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . 24 84 4.6. Hiding Information . . . . . . . . . . . . . . . . . . . 25 85 5. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 25 86 5.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 25 87 5.1.1. Destination Address . . . . . . . . . . . . . . . . . 25 88 5.1.2. Source Address . . . . . . . . . . . . . . . . . . . 25 89 5.2. Determining the Path . . . . . . . . . . . . . . . . . . 26 90 5.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 26 91 5.4. Last Hop Router (LHR) . . . . . . . . . . . . . . . . . . 26 92 5.5. First Hop Router (FHR) . . . . . . . . . . . . . . . . . 26 93 5.6. Broken Intermediate Router . . . . . . . . . . . . . . . 26 94 5.7. Non-Supported Router . . . . . . . . . . . . . . . . . . 27 95 5.8. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 27 96 5.8.1. Arriving at Source . . . . . . . . . . . . . . . . . 27 97 5.8.2. Fatal Error . . . . . . . . . . . . . . . . . . . . . 27 98 5.8.3. No Upstream Router . . . . . . . . . . . . . . . . . 27 99 5.8.4. Reply Timeout . . . . . . . . . . . . . . . . . . . . 27 100 5.9. Continuing after an Error . . . . . . . . . . . . . . . . 28 101 6. Protocol-Specific Considerations . . . . . . . . . . . . . . 28 102 6.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . 28 103 6.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . 28 104 6.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . 29 105 6.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . 29 106 7. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 29 107 7.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . 29 108 7.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 29 109 7.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 30 110 7.4. Link Utilization . . . . . . . . . . . . . . . . . . . . 30 111 7.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . 30 112 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 113 8.1. "Mtrace2 Forwarding Codes" Registry . . . . . . . . . . . 31 114 8.2. "Mtrace2 TLV Types" registry . . . . . . . . . . . . . . 31 115 8.3. UDP Destination Port . . . . . . . . . . . . . . . . . . 31 116 9. Security Considerations . . . . . . . . . . . . . . . . . . . 31 117 9.1. Addresses in Mtrace2 Header . . . . . . . . . . . . . . . 31 118 9.2. Filtering of Clients . . . . . . . . . . . . . . . . . . 31 119 9.3. Topology Discovery . . . . . . . . . . . . . . . . . . . 32 120 9.4. Characteristics of Multicast Channel . . . . . . . . . . 32 121 9.5. Limiting Query/Request Rates . . . . . . . . . . . . . . 32 122 9.6. Limiting Reply Rates . . . . . . . . . . . . . . . . . . 32 123 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32 124 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 33 125 11.1. Normative References . . . . . . . . . . . . . . . . . . 33 126 11.2. Informative References . . . . . . . . . . . . . . . . . 33 127 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 129 1. Introduction 131 Given a multicast distribution tree, tracing from a multicast source 132 to a receiver is difficult, since we do not know which branch of the 133 multicast tree the receiver lies. This means that we have to flood 134 the whole tree to find the path from a source to a receiver. On the 135 other hand, walking up the tree from a receiver to a source is easy, 136 as most existing multicast routing protocols know the upstream router 137 for each source. Tracing from a receiver to a source can involve 138 only the routers on the direct path. 140 This document specifies the multicast traceroute facility named 141 Mtrace version 2 or Mtrace2 which allows the tracing of an IP 142 multicast routing path. Mtrace2 is usually initiated from an Mtrace2 143 client by sending an Mtrace2 Query to a Last Hop Router (LHR) or to a 144 Rendezvous Point (RP). The RP is a special router where sources and 145 receivers meet in PIM-SM [5]. From the LHR/RP receiving the query, 146 the tracing is directed towards a specified source if a source 147 address is specified and source specific state exists on the 148 receiving router. If no source address is specified or if no source 149 specific state exists on a receiving LHR, the tracing is directed 150 toward the RP for the specified group address. Moreover, Mtrace2 151 provides additional information such as the packet rates and losses, 152 as well as other diagnostic information. Mtrace2 is primarily 153 intended for the following purposes: 155 o To trace the path that a packet would take from a source to a 156 receiver. 158 o To isolate packet loss problems (e.g., congestion). 160 o To isolate configuration problems (e.g., TTL threshold). 162 Figure 1 shows a typical case on how Mtrace2 is used. FHR represents 163 the first-hop router, LHR represents the last-hop router, and the 164 arrow lines represent the Mtrace2 messages that are sent from one 165 node to another. The numbers before the Mtrace2 messages represent 166 the sequence of the messages that would happen. Source, Receiver and 167 Mtrace2 client are typically hosts. 169 2. Request 2. Request 170 +----+ +----+ 171 | | | | 172 v | v | 173 +--------+ +-----+ +-----+ +----------+ 174 | Source |----| FHR |----- The Internet -----| LHR |----| Receiver | 175 +--------+ +-----+ | +-----+ +----------+ 176 \ | ^ 177 \ | / 178 \ | / 179 \ | / 180 3. Reply \ | / 1. Query 181 \ | / 182 \ | / 183 \ +---------+ / 184 v | Mtrace2 |/ 185 | client | 186 +---------+ 188 Figure 1 190 When an Mtrace2 client initiates a multicast trace, it sends an 191 Mtrace2 Query packet to the LHR or RP for a multicast group and, 192 optionally, a source address. The LHR/RP turns the Query packet into 193 a Request. The Request message type enables each of the upstream 194 routers processing the message to apply different packet and message 195 validation rules than those required for handling of a Query message. 196 The LHR/RP then appends a standard response block containing its 197 interface addresses and packet statistics to the Request packet, then 198 forwards the packet towards the source/RP. The Request packet is 199 either unicasted to its upstream router towards the source/RP, or 200 multicasted to the group if the upstream router's IP address is not 201 known. In a similar fashion, each router along the path to the 202 source/RP appends a standard response block to the end of the Request 203 packet before forwarding it to its upstream router. When the FHR 204 receives the Request packet, it appends its own standard response 205 block, turns the Request packet into a Reply, and unicasts the Reply 206 back to the Mtrace2 client. 208 The Mtrace2 Reply may be returned before reaching the FHR under some 209 circumstances. This can happen if a Request packet is received at an 210 RP or gateway, or when any of several types of error or exception 211 conditions occur which prevent sending of a request to the next 212 upstream router. 214 The Mtrace2 client waits for the Mtrace2 Reply message and displays 215 the results. When not receiving an Mtrace2 Reply message due to 216 network congestion, a broken router (see Section 5.6), or a non- 217 responding router (see Section 5.7), the Mtrace2 client may resend 218 another Mtrace2 Query with a lower hop count (see Section 3.2.1), and 219 repeat the process until it receives an Mtrace2 Reply message. The 220 details are Mtrace2 client specific, and it is outside the scope of 221 this document. 223 Note that when a router's control plane and forwarding plane are out 224 of sync, the Mtrace2 Requests might be forwarded based on the control 225 states instead. In which case, the traced path might not represent 226 the real path the data packets would follow. 228 Mtrace2 supports both IPv4 and IPv6. Unlike the previous version of 229 Mtrace, which implements its query and response as IGMP messages [8], 230 all Mtrace2 messages are UDP-based. Although the packet formats of 231 IPv4 and IPv6 Mtrace2 are different because of the address families, 232 the syntax between them is similar. 234 2. Terminology 236 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 237 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", 238 and "OPTIONAL" are to be interpreted as described in RFC 2119 [1], 239 and indicate requirement levels for compliant Mtrace2 240 implementations. 242 2.1. Definitions 244 Since Mtrace2 Queries and Requests flow in the opposite direction to 245 the data flow, we refer to "upstream" and "downstream" with respect 246 to data, unless explicitly specified. 248 Incoming interface 249 The interface on which data is expected to arrive from the 250 specified source and group. 252 Outgoing interface 253 This is one of the interfaces to which data from the source or RP 254 is expected to be transmitted for the specified source and group. 255 It is also the interface on which the Mtrace2 Request was 256 received. 258 Upstream router 259 The router, connecting to the Incoming interface of the current 260 router, which is responsible for forwarding data for the specified 261 source and group to the current router. 263 First-hop router (FHR) 264 The router that is directly connected to the source the Mtrace2 265 Query specifies. 267 Last-hop router (LHR) 268 A router that is directly connected to a receiver. It is also the 269 router that receives the Mtrace2 Query from an Mtrace2 client. 271 Group state 272 It is the state a shared-tree protocol, such as PIM-SM [5], uses 273 to choose the upstream router towards the RP for the specified 274 group. In this state, source-specific state is not available for 275 the corresponding group address on the router. 277 Source-specific state 278 It is the state that is used to choose the path towards the source 279 for the specified source and group. 281 ALL-[protocol]-ROUTERS.MCAST.NET 282 It is a link-local multicast address for multicast routers to 283 communicate with their adjacent routers that are running the same 284 routing protocol. For instance, the address of ALL-PIM- 285 ROUTERS.MCAST.NET [5] is '224.0.0.13' for IPv4 and 'ff02::d' for 286 IPv6. 288 3. Packet Formats 290 This section describes the details of the packet formats for Mtrace2 291 messages. 293 All Mtrace2 messages are encoded in TLV format (see Section 3.1). 294 The first TLV of a message is a message header TLV specifying the 295 type of message and additional context information required for 296 processing of the message and for parsing of subsequent TLVs in the 297 message. Subsequent TLVs in a message, referred to as Blocks, are 298 appended after the header TLV to provide additional information 299 associated with the message. If an implementation receives an 300 unknown TLV type for the first TLV in a message, it SHOULD ignore and 301 silently discard the TLV and any subsequent TLVs in the packet 302 containing the TLV. If an implementation receives an unknown TLV 303 type for a subsequent TLV within a message, it SHOULD ignore and 304 silently discard the TLV. If the length of a TLV exceeds the 305 available space in the containing packet, the implementation MUST 306 ignore and silently discard the TLV and any remaining portion of the 307 containing packet. Any data in the packet after the specified TLV 308 length is considered to be outside the boundary of the TLV and MUST 309 be ignored during processing of the TLV. 311 All Mtrace2 messages are UDP packets. For IPv4, Mtrace2 Query and 312 Request messages MUST NOT be fragmented. For IPv6, the packet size 313 for the Mtrace2 messages MUST NOT exceed 1280 bytes, which is the 314 smallest MTU for an IPv6 interface [2]. The source port is uniquely 315 selected by the local host operating system. The destination port is 316 the IANA reserved Mtrace2 port number (see Section 8). All Mtrace2 317 messages MUST have a valid UDP checksum. 319 Additionally, Mtrace2 supports both IPv4 and IPv6, but not mixed. 320 For example, if an Mtrace2 Query or Request message arrives in as an 321 IPv4 packet, all addresses specified in the Mtrace2 messages MUST be 322 IPv4 as well. Same rule applies to IPv6 Mtrace2 messages. 324 3.1. Mtrace2 TLV format 326 0 1 2 3 327 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 | Type | Length | Value .... | 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 332 Type: 8 bits 334 Describes the format of the Value field. For all the available 335 types, please see Section 3.2 337 Length: 16 bits 339 Length of Type, Length, and Value fields in octets. Minimum 340 length required is 3 octets. The maximum TLV length is not 341 defined; however the entire Mtrace2 packet length SHOULD NOT 342 exceed the available MTU. 344 Value: variable length 346 The format is based on the Type value. The length of the value 347 field is Length field minus 3. All reserved fields in the Value 348 field MUST be transmitted as zeros and ignored on receipt. 350 3.2. Defined TLVs 352 The following TLV Types are defined: 354 Code Type 355 ==== ================================ 356 0x01 Mtrace2 Query 357 0x02 Mtrace2 Request 358 0x03 Mtrace2 Reply 359 0x04 Mtrace2 Standard Response Block 360 0x05 Mtrace2 Augmented Response Block 361 0x06 Mtrace2 Extended Query Block 363 Each Mtrace2 message MUST begin with either a Query, Request or Reply 364 TLV. The first TLV determines the type of each Mtrace2 message. 365 Following a Query TLV, there can be a sequence of optional Extended 366 Query Blocks. In the case of a Request or a Reply TLV, it is then 367 followed by a sequence of Standard Response Blocks, each from a 368 multicast router on the path towards the source or the RP. In the 369 case more information is needed, a Standard Response Block can be 370 followed by one or multiple Augmented Response Blocks. 372 We will describe each message type in detail in the next few 373 sections. 375 3.2.1. Mtrace2 Query 377 An Mtrace2 Query is usually originated by an Mtrace2 client which 378 sends an Mtrace2 Query message to the LHR. When tracing towards the 379 source or the RP, the intermediate routers MUST NOT modify the Query 380 message except the Type field. 382 An Mtrace2 Query message is shown as follows: 384 0 1 2 3 385 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 386 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 387 | Type | Length | # Hops | 388 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 389 | | 390 | Multicast Address | 391 | | 392 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 393 | | 394 | Source Address | 395 | | 396 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 397 | | 398 | Mtrace2 Client Address | 399 | | 400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 401 | Query ID | Client Port # | 402 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 404 Figure 2 406 # Hops: 8 bits 407 This field specifies the maximum number of hops that the Mtrace2 408 client wants to trace. If there are some error conditions in the 409 middle of the path that prevent an Mtrace2 Reply from being 410 received by the client, the client MAY issue another Mtrace2 Query 411 with a lower number of hops until it receives a Reply. 413 Multicast Address: 32 bits or 128 bits 414 This field specifies an IPv4 or IPv6 address, which can be either: 416 m-1: a multicast group address to be traced; or, 418 m-2: all 1's in case of IPv4 or the unspecified address (::) in 419 case of IPv6 if no group-specific information is desired. 421 Source Address: 32 bits or 128 bits 422 This field specifies an IPv4 or IPv6 address, which can be either: 424 s-1: an unicast address of the source to be traced; or, 426 s-2: all 1's in case of IPv4 or the unspecified address (::) in 427 case of IPv6 if no source-specific information is desired. 428 For example, the client is tracing a (*,g) group state. 430 Note that it is invalid to have a source-group combination of 431 (s-2, m-2). If a router receives such combination in an Mtrace2 432 Query, it MUST silently discard the Query. 434 Mtrace2 Client Address: 32 bits or 128 bits 435 This field specifies the Mtrace2 client's IPv4 address or IPv6 436 global address. This address MUST be a valid unicast address, and 437 therefore, MUST NOT be all 1's or an unspecified address. The 438 Mtrace2 Reply will be sent to this address. 440 Query ID: 16 bits 441 This field is used as a unique identifier for this Mtrace2 Query 442 so that duplicate or delayed Reply messages may be detected. 444 Client Port #: 16 bits 445 This field specifies the destination UDP port number for receiving 446 the Mtrace2 Reply packet. 448 3.2.2. Mtrace2 Request 450 The format of an Mtrace2 Request message is similar to an Mtrace2 451 Query except the Type field is 0x02. 453 When a LHR receives an Mtrace2 Query message, it would turn the Query 454 into a Request by changing the Type field of the Query from 0x01 to 455 0x02. The LHR would then append an Mtrace2 Standard Response Block 456 (see Section 3.2.4) of its own to the Request message before sending 457 it upstream. The upstream routers would do the same without changing 458 the Type field until one of them is ready to send a Reply. 460 3.2.3. Mtrace2 Reply 462 The format of an Mtrace2 Reply message is similar to an Mtrace2 Query 463 except the Type field is 0x03. 465 When a FHR or a RP receives an Mtrace2 Request message which is 466 destined to itself, it would append an Mtrace2 Standard Response 467 Block (see Section 3.2.4) of its own to the Request message. Next, 468 it would turn the Request message into a Reply by changing the Type 469 field of the Request from 0x02 to 0x03. The Reply message would then 470 be unicasted to the Mtrace2 client specified in the Mtrace2 Client 471 Address field. 473 There are a number of cases an intermediate router might return a 474 Reply before a Request reaches the FHR or the RP. See Section 4.1.1, 475 Section 4.2.2, Section 4.3.3, and Section 4.5 for more details. 477 3.2.4. IPv4 Mtrace2 Standard Response Block 479 This section describes the message format of an IPv4 Mtrace2 Standard 480 Response Block. The Type field is 0x04. 482 0 1 2 3 483 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 484 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 485 | Type | Length | MBZ | 486 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 487 | Query Arrival Time | 488 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 489 | Incoming Interface Address | 490 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 491 | Outgoing Interface Address | 492 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 493 | Upstream Router Address | 494 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 495 | | 496 . Input packet count on incoming interface . 497 | | 498 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 499 | | 500 . Output packet count on outgoing interface . 501 | | 502 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 503 | | 504 . Total number of packets for this source-group pair . 505 | | 506 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 507 | Rtg Protocol | Multicast Rtg Protocol | 508 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 509 | Fwd TTL | MBZ |S| Src Mask |Forwarding Code| 510 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 512 MBZ: 8 bits 513 This field MUST be zeroed on transmission and ignored on 514 reception. 516 Query Arrival Time: 32 bits 517 The Query Arrival Time is a 32-bit NTP timestamp specifying the 518 arrival time of the Mtrace2 Query or Request packet at this 519 router. The 32-bit form of an NTP timestamp consists of the 520 middle 32 bits of the full 64-bit form; that is, the low 16 bits 521 of the integer part and the high 16 bits of the fractional part. 523 The following formula converts from a UNIX timeval to a 32-bit NTP 524 timestamp: 526 query_arrival_time 527 = (tv.tv_sec + 32384) << 16 + ((tv.tv_usec << 10) / 15625) 529 The constant 32384 is the number of seconds from Jan 1, 1900 to 530 Jan 1, 1970 truncated to 16 bits. ((tv.tv_usec << 10) / 15625) is 531 a reduction of ((tv.tv_usec / 100000000) << 16). 533 Note that Mtrace2 does not require all the routers on the path to 534 have synchronized clocks in order to measure one-way latency. 536 Additionally, Query Arrival Time is useful for measuring the 537 packet rate. For example, suppose that a client issues two 538 queries, and the corresponding requests R1 and R2 arrive at router 539 X at time T1 and T2, then the client would be able to compute the 540 packet rate on router X by using the packet count information 541 stored in the R1 and R2, and the time T1 and T2. 543 Incoming Interface Address: 32 bits 544 This field specifies the address of the interface on which packets 545 from the source or the RP are expected to arrive, or 0 if unknown 546 or unnumbered. 548 Outgoing Interface Address: 32 bits 549 This field specifies the address of the interface on which packets 550 from the source or the RP are expected to transmit towards the 551 receiver, or 0 if unknown or unnumbered. This is also the address 552 of the interface on which the Mtrace2 Query or Request arrives. 554 Upstream Router Address: 32 bits 555 This field specifies the address of the upstream router from which 556 this router expects packets from this source. This may be a 557 multicast group (e.g. ALL-[protocol]-ROUTERS.MCAST.NET) if the 558 upstream router is not known because of the workings of the 559 multicast routing protocol. However, it should be 0 if the 560 incoming interface address is unknown or unnumbered. 562 Input packet count on incoming interface: 64 bits 563 This field contains the number of multicast packets received for 564 all groups and sources on the incoming interface, or all 1's if no 565 count can be reported. This counter may have the same value as 566 ifHCInMulticastPkts from the IF-MIB [10] for this interface. 568 Output packet count on outgoing interface: 64 bit 569 This field contains the number of multicast packets that have been 570 transmitted or queued for transmission for all groups and sources 571 on the outgoing interface, or all 1's if no count can be reported. 572 This counter may have the same value as ifHCOutMulticastPkts from 573 the IF-MIB [10] for this interface. 575 Total number of packets for this source-group pair: 64 bits 576 This field counts the number of packets from the specified source 577 forwarded by the router to the specified group, or all 1's if no 578 count can be reported. If the S bit is set (see below), the count 579 is for the source network, as specified by the Src Mask field (see 580 below). If the S bit is set and the Src Mask field is 127, 581 indicating no source-specific state, the count is for all sources 582 sending to this group. This counter should have the same value as 583 ipMcastRoutePkts from the IPMROUTE-STD-MIB [11] for this 584 forwarding entry. 586 Rtg Protocol: 16 bits 587 This field describes the unicast routing protocol running between 588 this router and the upstream router, and it is used to determine 589 the RPF interface for the specified source or RP. This value 590 should have the same value as ipMcastRouteRtProtocol from the 591 IPMROUTE-STD-MIB [11] for this entry. If the router is not able 592 to obtain this value, all 0's must be specified. 594 Multicast Rtg Protocol: 16 bits 595 This field describes the multicast routing protocol in use between 596 the router and the upstream router. This value should have the 597 same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [11] 598 for this entry. If the router cannot obtain this value, all 0's 599 must be specified. 601 Fwd TTL: 8 bits 602 This field contains the configured multicast TTL threshold, if 603 any, of the outgoing interface. 605 S: 1 bit 606 If this bit is set, it indicates that the packet count for the 607 source-group pair is for the source network, as determined by 608 masking the source address with the Src Mask field. 610 Src Mask: 7 bits 611 This field contains the number of 1's in the netmask the router 612 has for the source (i.e. a value of 24 means the netmask is 613 0xffffff00). If the router is forwarding solely on group state, 614 this field is set to 127 (0x7f). 616 Forwarding Code: 8 bits 617 This field contains a forwarding information/error code. Values 618 with the high order bit set (0x80-0xff) are intended for use as 619 error or exception codes. Section 4.1 and Section 4.2 explain how 620 and when the Forwarding Code is filled. Defined values are as 621 follows: 623 Value Name Description 624 ----- -------------- ---------------------------------------------- 625 0x00 NO_ERROR No error 626 0x01 WRONG_IF Mtrace2 Request arrived on an interface 627 to which this router would not forward for 628 the specified group towards the source or RP. 629 0x02 PRUNE_SENT This router has sent a prune upstream which 630 applies to the source and group in the 631 Mtrace2 Request. 632 0x03 PRUNE_RCVD This router has stopped forwarding for this 633 source and group in response to a request 634 from the downstream router. 635 0x04 SCOPED The group is subject to administrative 636 scoping at this router. 637 0x05 NO_ROUTE This router has no route for the source or 638 group and no way to determine a potential 639 route. 640 0x06 WRONG_LAST_HOP This router is not the proper LHR. 641 0x07 NOT_FORWARDING This router is not forwarding this source and 642 group out the outgoing interface for an 643 unspecified reason. 644 0x08 REACHED_RP Reached the Rendezvous Point. 645 0x09 RPF_IF Mtrace2 Request arrived on the expected 646 RPF interface for this source and group. 647 0x0A NO_MULTICAST Mtrace2 Request arrived on an interface 648 which is not enabled for multicast. 649 0x0B INFO_HIDDEN One or more hops have been hidden from this 650 trace. 651 0x0C REACHED_GW Mtrace2 Request arrived on a gateway (e.g., 652 a NAT or firewall) that hides the 653 information between this router and the 654 Mtrace2 client. 655 0x0D UNKNOWN_QUERY A non-transitive Extended Query Type was 656 received by a router which does not support 657 the type. 658 0x80 FATAL_ERROR A fatal error is one where the router may 659 know the upstream router but cannot forward 660 the message to it. 661 0x81 NO_SPACE There was not enough room to insert another 662 Standard Response Block in the packet. 663 0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited. 665 3.2.5. IPv6 Mtrace2 Standard Response Block 667 This section describes the message format of an IPv6 Mtrace2 Standard 668 Response Block. The Type field is also 0x04. 670 0 1 2 3 671 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 672 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 673 | Type | Length | MBZ | 674 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 675 | Query Arrival Time | 676 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 677 | Incoming Interface ID | 678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 679 | Outgoing Interface ID | 680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 681 | | 682 * Local Address * 683 | | 684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 685 | | 686 * Remote Address * 687 | | 688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 689 | | 690 . Input packet count on incoming interface . 691 | | 692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 693 | | 694 . Output packet count on outgoing interface . 695 | | 696 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 697 | | 698 . Total number of packets for this source-group pair . 699 | | 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 | Rtg Protocol | Multicast Rtg Protocol | 702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 703 | MBZ 2 |S|Src Prefix Len |Forwarding Code| 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 706 MBZ: 8 bits 707 This field MUST be zeroed on transmission and ignored on 708 reception. 710 Query Arrival Time: 32 bits 711 Same definition as in IPv4. 713 Incoming Interface ID: 32 bits 714 This field specifies the interface ID on which packets from the 715 source or RP are expected to arrive, or 0 if unknown. This ID 716 should be the value taken from InterfaceIndex of the IF-MIB [10] 717 for this interface. 719 Outgoing Interface ID: 32 bits 720 This field specifies the interface ID to which packets from the 721 source or RP are expected to transmit, or 0 if unknown. This ID 722 should be the value taken from InterfaceIndex of the IF-MIB [10] 723 for this interface 725 Local Address: 128 bits 726 This field specifies a global IPv6 address that uniquely 727 identifies the router. An unique local unicast address [9] SHOULD 728 NOT be used unless the router is only assigned link-local and 729 unique local addresses. If the router is only assigned link-local 730 addresses, its link-local address can be specified in this field. 732 Remote Address: 128 bits 733 This field specifies the address of the upstream router, which, in 734 most cases, is a link-local unicast address for the upstream 735 router. 737 Although a link-local address does not have enough information to 738 identify a node, it is possible to detect the upstream router with 739 the assistance of Incoming Interface ID and the current router 740 address (i.e., Local Address). 742 Note that this may be a multicast group (e.g., ALL-[protocol]- 743 ROUTERS.MCAST.NET) if the upstream router is not known because of 744 the workings of a multicast routing protocol. However, it should 745 be the unspecified address (::) if the incoming interface address 746 is unknown. 748 Input packet count on incoming interface: 64 bits 749 Same definition as in IPv4. 751 Output packet count on outgoing interface: 64 bits 752 Same definition as in IPv4. 754 Total number of packets for this source-group pair: 64 bits 755 Same definition as in IPv4, except if the S bit is set (see 756 below), the count is for the source network, as specified by the 757 Src Prefix Len field. If the S bit is set and the Src Prefix Len 758 field is 255, indicating no source-specific state, the count is 759 for all sources sending to this group. This counter should have 760 the same value as ipMcastRoutePkts from the IPMROUTE-STD-MIB [11] 761 for this forwarding entry. 763 Rtg Protocol: 16 bits 764 Same definition as in IPv4. 766 Multicast Rtg Protocol: 16 bits 767 Same definition as in IPv4. 769 MBZ 2: 15 bits 770 This field MUST be zeroed on transmission and ignored on 771 reception. 773 S: 1 bit 774 Same definition as in IPv4, except the Src Prefix Len field is 775 used to mask the source address. 777 Src Prefix Len: 8 bits 778 This field contains the prefix length this router has for the 779 source. If the router is forwarding solely on group state, this 780 field is set to 255 (0xff). 782 Forwarding Code: 8 bits 783 Same definition as in IPv4. 785 3.2.6. Mtrace2 Augmented Response Block 787 In addition to the Standard Response Block, a multicast router on the 788 traced path can optionally add one or multiple Augmented Response 789 Blocks before sending the Request to its upstream router. 791 The Augmented Response Block is flexible for various purposes such as 792 providing diagnosis information (see Section 7) and protocol 793 verification. Its Type field is 0x05, and its format is as follows: 795 0 1 2 3 796 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 797 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 798 | Type | Length | MBZ | 799 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 800 | Augmented Response Type | Value .... | 801 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 803 MBZ: 8 bits 804 This field MUST be zeroed on transmission and ignored on 805 reception. 807 Augmented Response Type: 16 bits 808 This field specifies the type of various responses from a 809 multicast router that might need to communicate back to the 810 Mtrace2 client as well as the multicast routers on the traced 811 path. 813 The Augmented Response Type is defined as follows: 815 Code Type 816 ==== =============================================== 817 0x01 # of the returned Standard Response Blocks 819 When the NO_SPACE error occurs on a router, the router should send 820 the original Mtrace2 Request received from the downstream router 821 as a Reply back to the Mtrace2 client, and continue with a new 822 Mtrace2 Request. In the new Request, the router would add a 823 Standard Response Block followed by an Augmented Response Block 824 with 0x01 as the Augmented Response Type, and the number of the 825 returned Mtrace2 Standard Response Blocks as the Value. 827 Each upstream router would recognize the total number of hops the 828 Request has been traced so far by adding this number and the 829 number of the Standard Response Block in the current Request 830 message. 832 This document only defines one Augmented Response Type in the 833 Augmented Response Block. The description on how to provide 834 diagnosis information using the Augmented Response Block is out of 835 the scope of this document, and will be addressed in separate 836 documents. 838 Value: variable length 839 The format is based on the Augmented Response Type value. The 840 length of the value field is Length field minus 6. 842 3.2.7. Mtrace2 Extended Query Block 844 There may be a sequence of optional Extended Query Blocks that follow 845 an Mtrace2 Query to further specify any information needed for the 846 Query. For example, an Mtrace2 client might be interested in tracing 847 the path the specified source and group would take based on a certain 848 topology. In which case, the client can pass in the multi-topology 849 ID as the Value for an Extended Query Type (see below). The Extended 850 Query Type is extensible and the behavior of the new types will be 851 addressed by separate documents. 853 The Mtrace2 Extended Query Block's Type field is 0x06, and is 854 formatted as follows: 856 0 1 2 3 857 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 858 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 859 | Type | Length | MBZ |T| 860 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 861 | Extended Query Type | Value .... | 862 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 864 MBZ: 7 bits 865 This field MUST be zeroed on transmission and ignored on 866 reception. 868 T-bit (Transitive Attribute): 1 bit 869 If the TLV type is unrecognized by the receiving router, then this 870 TLV is either discarded or forwarded along with the Query, 871 depending on the value of this bit. If this bit is set, then the 872 router MUST forward this TLV. If this bit is clear, the router 873 MUST send an Mtrace2 Reply with an UNKNOWN_QUERY error. 875 Extended Query Type: 16 bits 876 This field specifies the type of the Extended Query Block. 878 Value: 16 bits 879 This field specifies the value of this Extended Query. 881 4. Router Behavior 883 This section describes the router behavior in the context of Mtrace2 884 in detail. 886 4.1. Receiving Mtrace2 Query 888 An Mtrace2 Query message is an Mtrace2 message with no response 889 blocks filled in, and uses TLV type of 0x01. 891 4.1.1. Query Packet Verification 893 Upon receiving an Mtrace2 Query message, a router MUST examine 894 whether the Multicast Address and the Source Address are a valid 895 combination as specified in Section 3.2.1, and whether the Mtrace2 896 Client Address is a valid IP unicast address. If either one is 897 invalid, the Query MUST be silently ignored. 899 Mtrace2 supports a non-local client to the LHR/RP. A router SHOULD, 900 however, support a mechanism to filter out queries from clients 901 beyond a specified administrative boundary. The potential approaches 902 are described in Section 9.2. 904 In the case where a local LHR client is required, the router must 905 then examine the Query to see if it is the proper LHR/RP for the 906 destination address in the packet. It is the proper local LHR if it 907 has a multicast-capable interface on the same subnet as the Mtrace2 908 Client Address and is the router that would forward traffic from the 909 given (S,G) or (*,G) onto that subnet. It is the proper RP if the 910 multicast group address specified in the query is 0 and if the IP 911 header destination address is a valid RP address on this router. 913 If the router determines that it is not the proper LHR/RP, or it 914 cannot make that determination, it does one of two things depending 915 on whether the Query was received via multicast or unicast. If the 916 Query was received via multicast, then it MUST be silently discarded. 917 If it was received via unicast, the router turns the Query into a 918 Reply message by changing the TLV type to 0x03 and appending a 919 Standard Response Block with a Forwarding Code of WRONG_LAST_HOP. 920 The rest of the fields in the Standard Response Block MUST be zeroed. 921 The router then sends the Reply message to the Mtrace2 Client Address 922 on the Client Port # as specified in the Mtrace2 Query. 924 Duplicate Query messages as identified by the tuple (Mtrace2 Client 925 Address, Query ID) SHOULD be ignored. This MAY be implemented using 926 a cache of previously processed queries keyed by the Mtrace2 Client 927 Address and Query ID pair. The duration of the cached entries is 928 implementation specific. Duplicate Request messages MUST NOT be 929 ignored in this manner. 931 4.1.2. Query Normal Processing 933 When a router receives an Mtrace2 Query and it determines that it is 934 the proper LHR/RP, it turns the Query to a Request by changing the 935 TLV type from 0x01 to 0x02, and performs the steps listed in 936 Section 4.2. 938 4.2. Receiving Mtrace2 Request 940 An Mtrace2 Request is an Mtrace2 message that uses TLV type of 0x02. 941 With the exception of the LHR, whose Request was just converted from 942 a Query, each Request received by a router should have at least one 943 Standard Response Block filled in. 945 4.2.1. Request Packet Verification 947 If the Mtrace2 Request does not come from an adjacent router, or if 948 the Request is not addressed to this router, or if the Request is 949 addressed to a multicast group which is not a link-scoped group (i.e. 950 224.0.0.0/24 for IPv4, FFx2::/16 [3] for IPv6), it MUST be silently 951 ignored. GTSM [12] SHOULD be used by the router to determine whether 952 the router is adjacent or not. 954 If the sum of the number of the Standard Response Blocks in the 955 received Mtrace2 Request and the value of the Augmented Response Type 956 of 0x01, if any, is equal or more than the # Hops in the Mtrace2 957 Request, it MUST be silently ignored. 959 4.2.2. Request Normal Processing 961 When a router receives an Mtrace2 Request message, it performs the 962 following steps. Note that it is possible to have multiple 963 situations covered by the Forwarding Codes. The first one 964 encountered is the one that is reported, i.e. all "note Forwarding 965 Code N" should be interpreted as "if Forwarding Code is not already 966 set, set Forwarding Code to N". Note that in the steps described 967 below the "Outgoing Interface" is the one on which the Mtrace2 968 Request message arrives. 970 1. Prepare a Standard Response Block to be appended to the packet, 971 setting all fields to an initial default value of zero. 973 2. If Mtrace2 is administratively prohibited, note the Forwarding 974 Code of ADMIN_PROHIB and skip to step 4. 976 3. In the Standard Response Block, fill in the Query Arrival Time, 977 Outgoing Interface Address (for IPv4) or Outgoing Interface ID 978 (for IPv6), Output Packet Count, and Fwd TTL (for IPv4). 980 4. Attempt to determine the forwarding information for the 981 specified source and group, using the same mechanisms as would 982 be used when a packet is received from the source destined for 983 the group. A state need not be instantiated, it can be a 984 "phantom" state created only for the purpose of the trace, such 985 as "dry-run." 987 If using a shared-tree protocol and there is no source-specific 988 state, or if no source-specific information is desired (i.e., 989 all 1's for IPv4 or unspecified address (::) for IPv6), group 990 state should be used. If there is no group state or no group- 991 specific information is desired, potential source state (i.e., 992 the path that would be followed for a source-specific Join) 993 should be used. 995 5. If no forwarding information can be determined, the router notes 996 a Forwarding Code of NO_ROUTE, sets the remaining fields that 997 have not yet been filled in to zero, and then sends an Mtrace2 998 Reply back to the Mtrace2 client. 1000 6. If a Forwarding Code of ADMIN_PROHIB has been set, skip to step 1001 7. Otherwise, fill in the Incoming Interface Address (or 1002 Incoming Interface ID and Local Address for IPv6), Upstream 1003 Router Address (or Remote Address for IPv6), Input Packet Count, 1004 Total Number of Packets, Routing Protocol, S, and Src Mask (or 1005 Src Prefix Len for IPv6) using the forwarding information 1006 determined in step 4. 1008 7. If the Outgoing interface is not enabled for multicast, note 1009 Forwarding Code of NO_MULTICAST. If the Outgoing interface is 1010 the interface from which the router would expect data to arrive 1011 from the source, note forwarding code RPF_IF. If the Outgoing 1012 interface is not one to which the router would forward data from 1013 the source or RP to the group, a Forwarding code of WRONG_IF is 1014 noted. In the above three cases, the router will return an 1015 Mtrace2 Reply and terminate the trace. 1017 8. If the group is subject to administrative scoping on either the 1018 Outgoing or Incoming interfaces, a Forwarding Code of SCOPED is 1019 noted. 1021 9. If this router is the RP for the group for a non-source-specific 1022 query, note a Forwarding Code of REACHED_RP. The router will 1023 send an Mtrace2 Reply and terminate the trace. 1025 10. If this router is directly connected to the specified source or 1026 source network on the Incoming interface, it sets the Upstream 1027 Router Address (for IPv4) or the Remote Address (for IPv6) of 1028 the response block to zero. The router will send an Mtrace2 1029 Reply and terminate the trace. 1031 11. If this router has sent a prune upstream which applies to the 1032 source and group in the Mtrace2 Request, it notes a Forwarding 1033 Code of PRUNE_SENT. If the router has stopped forwarding 1034 downstream in response to a prune sent by the downstream router, 1035 it notes a Forwarding Code of PRUNE_RCVD. If the router should 1036 normally forward traffic downstream for this source and group 1037 but is not, it notes a Forwarding Code of NOT_FORWARDING. 1039 12. If this router is a gateway (e.g., a NAT or firewall) that hides 1040 the information between this router and the Mtrace2 client, it 1041 notes a Forwarding Code of REACHED_GW. The router continues the 1042 processing as described in Section 4.5. 1044 13. If the total number of the Standard Response Blocks, including 1045 the newly prepared one, and the value of the Augmented Response 1046 Type of 0x01, if any, is less than the # Hops in the Request, 1047 the packet is then forwarded to the upstream router as described 1048 in Section 4.3; otherwise, the packet is sent as an Mtrace2 1049 Reply to the Mtrace2 client as described in Section 4.4. 1051 4.3. Forwarding Mtrace2 Request 1053 This section describes how an Mtrace2 Request should be forwarded. 1055 4.3.1. Destination Address 1057 If the upstream router for the Mtrace2 Request is known for this 1058 request, the Mtrace2 Request is sent to that router. If the Incoming 1059 interface is known but the upstream router is not, the Mtrace2 1060 Request is sent to an appropriate multicast address on the Incoming 1061 interface. The multicast address SHOULD depend on the multicast 1062 routing protocol in use, such as ALL-[protocol]-ROUTERS.MCAST.NET. 1063 It MUST be a link-scoped group (i.e. 224.0.0.0/24 for IPv4, FF02::/16 1064 for IPv6), and MUST NOT be ALL-SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 1065 and All Nodes Address (FF02::1) for IPv6. It MAY also be ALL- 1066 ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers Address 1067 (FF02::2) for IPv6 if the routing protocol in use does not define a 1068 more appropriate multicast address. 1070 4.3.2. Source Address 1072 An Mtrace2 Request should be sent with the address of the Incoming 1073 interface. However, if the Incoming interface is unnumbered, the 1074 router can use one of its numbered interface addresses as the source 1075 address. 1077 4.3.3. Appending Standard Response Block 1079 An Mtrace2 Request MUST be sent upstream towards the source or the RP 1080 after appending a Standard Response Block to the end of the received 1081 Mtrace2 Request. The Standard Response Block includes the multicast 1082 states and statistics information of the router described in 1083 Section 3.2.4. 1085 If appending the Standard Response Block would make the Mtrace2 1086 Request packet longer than the MTU of the Incoming Interface, or, in 1087 the case of IPv6, longer than 1280 bytes, the router MUST change the 1088 Forwarding Code in the last Standard Response Block of the received 1089 Mtrace2 Request into NO_SPACE. The router then turns the Request 1090 into a Reply, and sends the Reply as described in Section 4.4. 1092 The router will continue with a new Request by copying from the old 1093 Request excluding all the response blocks, followed by the previously 1094 prepared Standard Response Block, and an Augmented Response Block 1095 with Augmented Response Type of 0x01 and the number of the returned 1096 Standard Response Blocks as the value. The new Request is then 1097 forwarded upstream. 1099 4.4. Sending Mtrace2 Reply 1101 An Mtrace2 Reply MUST be returned to the client by a router if the 1102 total number of the traced routers is equal to the # Hops in the 1103 Request. The total number of the traced routers is the sum of the 1104 Standard Response Blocks in the Request (including the one just 1105 added) and the number of the returned blocks, if any. 1107 4.4.1. Destination Address 1109 An Mtrace2 Reply MUST be sent to the address specified in the Mtrace2 1110 Client Address field in the Mtrace2 Request. 1112 4.4.2. Source Address 1114 An Mtrace2 Reply SHOULD be sent with the address of the router's 1115 Outgoing interface. However, if the Outgoing interface address is 1116 unnumbered, the router can use one of its numbered interface 1117 addresses as the source address. 1119 4.4.3. Appending Standard Response Block 1121 An Mtrace2 Reply MUST be sent with the prepared Standard Response 1122 Block appended at the end of the received Mtrace2 Request except in 1123 the case of NO_SPACE forwarding code. 1125 4.5. Proxying Mtrace2 Query 1127 When a gateway (e.g., a NAT or firewall), which needs to block 1128 unicast packets to the Mtrace2 client, or hide information between 1129 the gateway and the Mtrace2 client, receives an Mtrace2 Query from an 1130 adjacent host or Mtrace2 Request from an adjacent router, it appends 1131 a Standard Response Block with REACHED_GW as the Forwarding Code. It 1132 turns the Query or Request into a Reply, and sends the Reply back to 1133 the client. 1135 At the same time, the gateway originates a new Mtrace2 Query message 1136 by copying the original Mtrace2 header (the Query or Request without 1137 any of the response blocks), and makes the changes as follows: 1139 o sets the RPF interface's address as the Mtrace2 Client Address; 1141 o uses its own port number as the Client Port #; and, 1143 o decreases # Hops by ((number of the Standard Response Blocks that 1144 were just returned in a Reply) - 1). The "-1" in this expression 1145 accounts for the additional Standard Response Block appended by 1146 the gateway router. 1148 The new Mtrace2 Query message is then sent to the upstream router or 1149 to an appropriate multicast address on the RPF interface. 1151 When the gateway receives an Mtrace2 Reply whose Query ID matches the 1152 one in the original Mtrace2 header, it MUST relay the Mtrace2 Reply 1153 back to the Mtrace2 client by replacing the Reply's header with the 1154 original Mtrace2 header. If the gateway does not receive the 1155 corresponding Mtrace2 Reply within the [Mtrace Reply Timeout] period 1156 (see Section 5.8.4), then it silently discards the original Mtrace2 1157 Query or Request message, and terminates the trace. 1159 4.6. Hiding Information 1161 Information about a domain's topology and connectivity may be hidden 1162 from the Mtrace2 Requests. The Forwarding Code of INFO_HIDDEN may be 1163 used to note that. For example, the incoming interface address and 1164 packet count on the ingress router of a domain, and the outgoing 1165 interface address and packet count on the egress router of the domain 1166 can be specified as all 1's. Additionally, the source-group packet 1167 count (see Section 3.2.4 and Section 3.2.5) within the domain may be 1168 all 1's if it is hidden. 1170 5. Client Behavior 1172 This section describes the behavior of an Mtrace2 client in detail. 1174 5.1. Sending Mtrace2 Query 1176 An Mtrace2 client initiates an Mtrace2 Query by sending the Query to 1177 the LHR of interest. 1179 5.1.1. Destination Address 1181 If an Mtrace2 client knows the proper LHR, it unicasts an Mtrace2 1182 Query packet to that router; otherwise, it MAY send the Mtrace2 Query 1183 packet to the ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All 1184 Routers Address (FF02::2) for IPv6. This will ensure that the packet 1185 is received by the LHR on the subnet. 1187 See also Section 5.4 on determining the LHR. 1189 5.1.2. Source Address 1191 An Mtrace2 Query MUST be sent with the client's interface address, 1192 which would be the Mtrace2 Client Address. 1194 5.2. Determining the Path 1196 An Mtrace2 client could send an initial Query messages with a large # 1197 Hops, in order to try to trace the full path. If this attempt fails, 1198 one strategy is to perform a linear search (as the traditional 1199 unicast traceroute program does); set the # Hops field to 1 and try 1200 to get a Reply, then 2, and so on. If no Reply is received at a 1201 certain hop, the hop count can continue past the non-responding hop, 1202 in the hopes that further hops may respond. These attempts should 1203 continue until the [Mtrace Reply Timeout] timeout has occurred. 1205 See also Section 5.6 on receiving the results of a trace. 1207 5.3. Collecting Statistics 1209 After a client has determined that it has traced the whole path or as 1210 much as it can expect to (see Section 5.8), it might collect 1211 statistics by waiting a short time and performing a second trace. If 1212 the path is the same in the two traces, statistics can be displayed 1213 as described in Section 7.3 and Section 7.4. 1215 5.4. Last Hop Router (LHR) 1217 The Mtrace2 client may not know which is the last-hop router, or that 1218 router may be behind a firewall that blocks unicast packets but 1219 passes multicast packets. In these cases, the Mtrace2 Request should 1220 be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All 1221 Routers Address (FF02::2) for IPv6. All routers except the correct 1222 last-hop router SHOULD ignore any Mtrace2 Request received via 1223 multicast. 1225 5.5. First Hop Router (FHR) 1227 The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default 1228 multicast group for old IPv4 mtrace (v1) responses, in order to 1229 support mtrace clients that are not unicast reachable from the first- 1230 hop router. Mtrace2, however, does not require any IPv4/IPv6 1231 multicast addresses for the Mtrace2 Replies. Every Mtrace2 Reply is 1232 sent to the unicast address specified in the Mtrace2 Client Address 1233 field of the Mtrace2 Reply. 1235 5.6. Broken Intermediate Router 1237 A broken intermediate router might simply not understand Mtrace2 1238 packets, and drop them. The Mtrace2 client will get no Reply at all 1239 as a result. It should then perform a hop-by-hop search by setting 1240 the # Hops field until it gets an Mtrace2 Reply. The client may use 1241 linear or binary search; however, the latter is likely to be slower 1242 because a failure requires waiting for the [Mtrace Reply Timeout] 1243 period. 1245 5.7. Non-Supported Router 1247 When a non-supported router receives an Mtrace2 Query or Request 1248 message whose destination address is a multicast address, the router 1249 will silently discard the message. 1251 When the router receives an Mtrace2 Query which is destined to 1252 itself, the router would return an ICMP port unreachable to the 1253 Mtrace2 client. On the other hand, when the router receives an 1254 Mtrace2 Request which is destined to itself, the router would return 1255 an ICMP port unreachable to its adjacent router from which the 1256 Request receives. Therefore, the Mtrace2 client needs to terminate 1257 the trace when the [Mtrace Reply Timeout] timeout has occurred, and 1258 may then issue another Query with a lower number of # Hops. 1260 5.8. Mtrace2 Termination 1262 When performing an expanding hop-by-hop trace, it is necessary to 1263 determine when to stop expanding. 1265 5.8.1. Arriving at Source 1267 A trace can be determined to have arrived at the source if the 1268 Incoming Interface of the last router in the trace is non-zero, but 1269 the Upstream Router is zero. 1271 5.8.2. Fatal Error 1273 A trace has encountered a fatal error if the last Forwarding Error in 1274 the trace has the 0x80 bit set. 1276 5.8.3. No Upstream Router 1278 A trace can not continue if the last Upstream Router in the trace is 1279 set to 0. 1281 5.8.4. Reply Timeout 1283 This document defines the [Mtrace Reply Timeout] value, which is used 1284 to time out an Mtrace2 Reply as seen in Section 4.5, Section 5.2, and 1285 Section 5.7. The default [Mtrace Reply Timeout] value is 10 1286 (seconds), and can be manually changed on the Mtrace2 client and 1287 routers. 1289 5.9. Continuing after an Error 1291 When the NO_SPACE error occurs, as described in Section 4.2, a router 1292 will send back an Mtrace2 Reply to the Mtrace2 client, and continue 1293 with a new Request (see Section 4.3.3). In which case, the Mtrace2 1294 client may receive multiple Mtrace2 Replies from different routers 1295 along the path. When this happens, the client MUST treat them as a 1296 single Mtrace2 Reply message. 1298 If a trace times out, it is very likely that a router in the middle 1299 of the path does not support Mtrace2. That router's address will be 1300 in the Upstream Router field of the last Standard Response Block in 1301 the last received Reply. A client may be able to determine (via 1302 mrinfo or SNMP [9][11]) a list of neighbors of the non-responding 1303 router. If desired, each of those neighbors could be probed to 1304 determine the remainder of the path. Unfortunately, this heuristic 1305 may end up with multiple paths, since there is no way of knowing what 1306 the non-responding router's algorithm for choosing an upstream router 1307 is. However, if all paths but one flow back towards the non- 1308 responding router, it is possible to be sure that this is the correct 1309 path. 1311 6. Protocol-Specific Considerations 1313 This section describes the Mtrace2 behavior with the presence of 1314 different multicast protocols. 1316 6.1. PIM-SM 1318 When an Mtrace2 reaches a PIM-SM RP, and the RP does not forward the 1319 trace on, it means that the RP has not performed a source-specific 1320 join so there is no more state to trace. However, the path that 1321 traffic would use if the RP did perform a source-specific join can be 1322 traced by setting the trace destination to the RP, the trace source 1323 to the traffic source, and the trace group to 0. This Mtrace2 Query 1324 may be unicasted to the RP, and the RP takes the same actions as an 1325 LHR. 1327 6.2. Bi-Directional PIM 1329 Bi-directional PIM [6] is a variant of PIM-SM that builds bi- 1330 directional shared trees connecting multicast sources and receivers. 1331 Along the bi-directional shared trees, multicast data is natively 1332 forwarded from the sources to the Rendezvous Point Link (RPL), and 1333 from which, to receivers without requiring source-specific state. In 1334 contrast to PIM-SM, Bi-directional PIM always has the state to trace. 1336 A Designated Forwarder (DF) for a given Rendezvous Point Address 1337 (RPA) is in charge of forwarding downstream traffic onto its link, 1338 and forwarding upstream traffic from its link towards the RPL that 1339 the RPA belongs to. Hence Mtrace2 Reply reports DF addresses or RPA 1340 along the path. 1342 6.3. PIM-DM 1344 Routers running PIM Dense Mode [13] do not know the path packets 1345 would take unless traffic is flowing. Without some extra protocol 1346 mechanism, this means that in an environment with multiple possible 1347 paths with branch points on shared media, Mtrace2 can only trace 1348 existing paths, not potential paths. When there are multiple 1349 possible paths but the branch points are not on shared media, the 1350 upstream router is known, but the LHR may not know that it is the 1351 appropriate last hop. 1353 When traffic is flowing, PIM Dense Mode routers know whether or not 1354 they are the LHR for the link (because they won or lost an Assert 1355 battle) and know who the upstream router is (because it won an Assert 1356 battle). Therefore, Mtrace2 is always able to follow the proper path 1357 when traffic is flowing. 1359 6.4. IGMP/MLD Proxy 1361 When an IGMP/MLD Proxy [7] receives an Mtrace2 Query packet on an 1362 incoming interface, it notes a WRONG_IF in the Forwarding Code of the 1363 last Standard Response Block (see Section 3.2.4), and sends the 1364 Mtrace2 Reply back to the Mtrace2 client. On the other hand, when an 1365 Mtrace2 Query packet reaches an outgoing interface of the IGMP/MLD 1366 proxy, it is forwarded onto its incoming interface towards the 1367 upstream router. 1369 7. Problem Diagnosis 1371 This section describes different scenarios Mtrace2 can be used to 1372 diagnose the multicast problems. 1374 7.1. Forwarding Inconsistencies 1376 The Forwarding Error code can tell if a group is unexpectedly pruned 1377 or administratively scoped. 1379 7.2. TTL or Hop Limit Problems 1381 By taking the maximum of hops from the source and forwarding TTL 1382 threshold over all hops, it is possible to discover the TTL or hop 1383 limit required for the source to reach the destination. 1385 7.3. Packet Loss 1387 By taking two traces, it is possible to find packet loss information 1388 by comparing the difference in input packet counts to the difference 1389 in output packet counts for the specified source-group address pair 1390 at the previous hop. On a point-to-point link, any difference in 1391 these numbers implies packet loss. Since the packet counts may be 1392 changing as the Mtrace2 Request is propagating, there may be small 1393 errors (off by 1 or 2 or more) in these statistics. However, these 1394 errors will not accumulate if multiple traces are taken to expand the 1395 measurement period. On a shared link, the count of input packets can 1396 be larger than the number of output packets at the previous hop, due 1397 to other routers or hosts on the link injecting packets. This 1398 appears as "negative loss" which may mask real packet loss. 1400 In addition to the counts of input and output packets for all 1401 multicast traffic on the interfaces, the Standard Response Block 1402 includes a count of the packets forwarded by a node for the specified 1403 source-group pair. Taking the difference in this count between two 1404 traces and then comparing those differences between two hops gives a 1405 measure of packet loss just for traffic from the specified source to 1406 the specified receiver via the specified group. This measure is not 1407 affected by shared links. 1409 On a point-to-point link that is a multicast tunnel, packet loss is 1410 usually due to congestion in unicast routers along the path of that 1411 tunnel. On native multicast links, loss is more likely in the output 1412 queue of one hop, perhaps due to priority dropping, or in the input 1413 queue at the next hop. The counters in the Standard Response Block 1414 do not allow these cases to be distinguished. Differences in packet 1415 counts between the incoming and outgoing interfaces on one node 1416 cannot generally be used to measure queue overflow in the node. 1418 7.4. Link Utilization 1420 Again, with two traces, you can divide the difference in the input or 1421 output packet counts at some hop by the difference in time stamps 1422 from the same hop to obtain the packet rate over the link. If the 1423 average packet size is known, then the link utilization can also be 1424 estimated to see whether packet loss may be due to the rate limit or 1425 the physical capacity on a particular link being exceeded. 1427 7.5. Time Delay 1429 If the routers have synchronized clocks, it is possible to estimate 1430 propagation and queuing delay from the differences between the 1431 timestamps at successive hops. However, this delay includes control 1432 processing overhead, so is not necessarily indicative of the delay 1433 that data traffic would experience. 1435 8. IANA Considerations 1437 The following new registries are to be created and maintained under 1438 the "RFC Required" registry policy as specified in [4]. 1440 8.1. "Mtrace2 Forwarding Codes" Registry 1442 This is an integer in the range 0-255. Assignment of a Forwarding 1443 Code requires specification of a value and a name for the Forwarding 1444 Code. Initial values for the forwarding codes are given in the table 1445 at the end of Section 3.2.4. Additional values (specific to IPv6) 1446 may also be specified at the end of Section 3.2.5. Any additions to 1447 this registry are required to fully describe the conditions under 1448 which the new Forwarding Code is used. 1450 8.2. "Mtrace2 TLV Types" registry 1452 Assignment of a TLV Type requires specification of an integer value 1453 "Code" in the range 0-255 and a name ("Type"). Initial values for 1454 the TLV Types are given in the table at the beginning of Section 3.2. 1456 8.3. UDP Destination Port 1458 The Mtrace2 UDP destination port is [TBD]. 1460 9. Security Considerations 1462 This section addresses some of the security considerations related to 1463 Mtrace2. 1465 9.1. Addresses in Mtrace2 Header 1467 An Mtrace2 header includes three addresses, source address, multicast 1468 address, and Mtrace2 client address. These addresses MUST be 1469 congruent with the definition defined in Section 3.2.1 and forwarding 1470 Mtrace2 messages having invalid addresses MUST be prohibited. For 1471 instance, if Mtrace2 Client Address specified in an Mtrace2 header is 1472 a multicast address, then a router that receives the Mtrace2 message 1473 MUST silently discard it. 1475 9.2. Filtering of Clients 1477 A router SHOULD support a mechanism to filter out queries from 1478 clients beyond a specified administrative boundary. Such a boundary 1479 could, for example, be specified via a list of allowed/disallowed 1480 client addresses or subnets. If a query is received from beyond the 1481 specified administrative boundary, the Query MUST NOT be processed. 1482 The router MAY, however, perform rate limited logging of such events. 1484 9.3. Topology Discovery 1486 Mtrace2 can be used to discover any actively-used topology. If your 1487 network topology is a secret, Mtrace2 may be restricted at the border 1488 of your domain, using the ADMIN_PROHIB forwarding code. 1490 9.4. Characteristics of Multicast Channel 1492 Mtrace2 can be used to discover what sources are sending to what 1493 groups and at what rates. If this information is a secret, Mtrace2 1494 may be restricted at the border of your domain, using the 1495 ADMIN_PROHIB forwarding code. 1497 9.5. Limiting Query/Request Rates 1499 A router may limit Mtrace2 Queries and Requests by ignoring some of 1500 the consecutive messages. The router MAY randomly ignore the 1501 received messages to minimize the processing overhead, i.e., to keep 1502 fairness in processing queries, or prevent traffic amplification. 1503 The rate limit is left to the router's implementation. 1505 9.6. Limiting Reply Rates 1507 The proxying and NO_SPACE behaviors may result in one Query returning 1508 multiple Reply messages. In order to prevent abuse, the routers in 1509 the traced path MAY need to rate-limit the Replies. The rate limit 1510 function is left to the router's implementation. 1512 10. Acknowledgements 1514 This specification started largely as a transcription of Van 1515 Jacobson's slides from the 30th IETF, and the implementation in 1516 mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve 1517 Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original 1518 multicast traceroute client, mtrace (version 1), has been implemented 1519 by Ajit Thyagarajan, Steve Casner and Bill Fenner. The idea of the 1520 "S" bit to allow statistics for a source subnet is due to Tom 1521 Pusateri. 1523 For the Mtrace version 2 specification, the authors would like to 1524 give special thanks to Tatsuya Jinmei, Bill Fenner, and Steve Casner. 1525 Also, extensive comments were received from David L. Black, Ronald 1526 Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Robert Kebler, John 1527 Kristoff, Heidi Ou, Pekka Savola, Shinsuke Suzuki, Dave Thaler, 1528 Achmad Husni Thamrin, Stig Venaas, and Cao Wei. 1530 11. References 1532 11.1. Normative References 1534 [1] Bradner, S., "Key words for use in RFCs to indicate 1535 requirement levels", RFC 2119, March 1997. 1537 [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1538 (IPv6) Specification", RFC 2460, December 1998. 1540 [3] Hinden, R. and S. Deering, "IP Version 6 Addressing 1541 Architecture", RFC 4291, February 2006. 1543 [4] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1544 IANA Considerations Section in RFCs", RFC 5226, May 2008. 1546 [5] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 1547 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 1548 Protocol Specification (Revised)", RFC 4601, August 2006. 1550 [6] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1551 "Bidirectional Protocol Independent Multicast (BIDIR- 1552 PIM)", RFC 5015, October 2007. 1554 [7] Fenner, B., He, H., Haberman, B., and H. Sandick, 1555 "Internet Group Management Protocol (IGMP) / Multicast 1556 Listener Discovery (MLD)-Based Multicast Forwarding 1557 ("IGMP/MLD Proxying")", RFC 4605, August 2006. 1559 11.2. Informative References 1561 [8] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 1562 Thyagarajan, "Internet Group Management Protocol, Version 1563 3", RFC 3376, October 2002. 1565 [9] Draves, R. and D. Thaler, "Default Router Preferences and 1566 More-Specific Routes", RFC 4191, November 2005. 1568 [10] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 1569 MIB", RFC 2863, June 2000. 1571 [11] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast 1572 MIB", RFC 5132, December 2007. 1574 [12] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. 1575 Pignataro, "The Generalized TTL Security Mechanism 1576 (GTSM)", RFC 5082, October 2007. 1578 [13] Adams, A., Nicholas, J., and W. Siadak, "Protocol 1579 Independent Multicast - Dense Mode (PIM-DM): Protocol 1580 Specification (Revised)", RFC 3973, January 2005. 1582 Authors' Addresses 1584 Hitoshi Asaeda 1585 National Institute of Information and Communications Technology 1586 4-2-1 Nukui-Kitamachi 1587 Koganei, Tokyo 184-8795 1588 Japan 1590 Email: asaeda@nict.go.jp 1592 Kerry Meyer 1593 Cisco Systems, Inc. 1594 510 McCarthy Blvd. 1595 Milpitas, CA 95035 1596 USA 1598 Email: kerrymey@cisco.com 1600 WeeSan Lee (editor) 1602 Email: weesan@weesan.com